Method and apparatus for selectively curing a sheet of EPDM material

ABSTRACT

A method and apparatus for selectively curing a sheet of ethylene-propylene diene termonomer (EPDM) material to form a roofing membrane for installation on a roof deck. The method includes the steps of providing a sheet formed of ethylene-propylene diene termonomer, the sheet having a field and longitudinal edge areas bordering the field; and then simultaneously shielding at least one edge area of the EPDM sheet and exposing at least the field to a source of radiation to cure at least the field of the EPDM sheet and provide a selectively cured EPDM roofing membrane. Also disclosed is the product formed by the method of the present invention.

FIELD OF THE INVENTION

[0001] This invention relates to a method and apparatus for selectivelycuring a sheet of ethylene-propylene diene termonomer (EPDM) materialand the product formed thereby. More particularly, this inventionrelates to a method and apparatus for selectively curing at least thefield portion of a sheet of EPDM material for use as a roofing membraneand to a method of joining the roofing membranes and the product formedthereby.

BACKGROUND OF THE INVENTION

[0002] EPDM membranes are used as a single ply roofing material forindustrial and commercial flat roofs. Such membranes are generallyapplied to the roof surface in a vulcanized or cured state. Because ofoutstanding weather resistance and flexibility, cured EPDM roofingmembrane material has rapidly gained acceptance. The material istypically prepared by vulcanizing the composition in the presence ofsulfur or sulfur containing compounds such as mercaptans or by usingradiation cross linking promoters in the EPDM material which can becured by ionizing radiation, for example, see U.S. Pat. No. 4,803,020,incorporated herein by reference.

[0003] Notwithstanding the usefulness of radiation curing and sulfurcuring of a sheet of EPDM, a disadvantage of utilizing EPDM material isthe lack of adhesion of cured EPDM to itself Accordingly, it is usuallynecessary to splice the cured EPDM roofing membranes together with anadhesive to bond the cured EPDM membranes together to form a continuousEPDM membrane to cover the roof. It will be appreciated that the use ofan adhesive for splicing cured EPDM membranes together requires that theadhesive and the resulting bond must meet a number of requirements whichare extremely difficult to satisfy. The adhesive must provide sufficientseam peel and shear strength to permit the splice formed by bonding thecured EPDM membranes together to resist both the short-term andlong-term stresses experienced by the spliced EPDM roofing membrane.

[0004] In view of the foregoing, it is an object of the presentinvention to provide a method and apparatus for selectively curing onlythe field of a sheet of EPDM. It is another object of the presentinvention to provide a method and apparatus for selectively curing onlythe field of a sheet of EPDM with radiation, preferably infraredradiation, and to a method of joining at least two selectively curedEPDM membranes to form a larger membrane. Yet another object of thepresent invention is to provide a method of splicing selectively curedEPDM membranes having a cured field and uncured longitudinal edge areawhich eliminates the need for a solvent based or non-solvent basedsplicing adhesive along the overlapping edge area and the related laborand hardware necessary for mixing and application thereof. It is anotherobject of the present invention to provide a method and apparatus forcuring only the field of a sheet of EPDM that is simple and economical.

SUMMARY OF THE INVENTION

[0005] Briefly, according to the present invention there is provided amethod and apparatus for selectively curing a sheet of EPDM to form aroofing membrane for installation on a roof deck. The method includesthe steps of providing a sheet formed of ethylene-propylene dienetermonomer, the sheet having a field and longitudinal edge portionsbordering the field. The field is defined by a planar surface portionexclusive of the longitudinal edge portions. The longitudinal edgeportions are defined by the extent of overlap of adjacent roofingmembranes when installed on a roof deck. The sheet is then selectivelycured such that at least only the field is cured thereby leaving atleast one longitudinal edge portion of the sheet uncured.

[0006] The apparatus for selectively curing a sheet ofethylene-propylene diene termonomer (EPDM) defined by a field andlongitudinal edge areas bordering the field includes a curing oven, aradiation source and at least one screen. The curing oven has a roof anda floor interconnected by sidewalls, a front end and a back end. Thefront end includes an entrance and the back end includes an exit. Aconveyor is positioned between the front end and the back end of thecuring oven for continuously conveying the sheet of EPDM through thecuring oven. The radiation source is located above the conveyor withinthe curing oven. At least one screen operatively projects from eachsidewall of the curing oven and extends the longitudinal length of thecuring oven to cover at least one edge area of the sheet and shield theedge area of the sheet of EPDM as the sheet passes through the curingoven under the radiation source.

[0007] The resulting roofing membrane from the process of the presentinvention is a sheet formed of ethylene-propylene diene termonomer. Thesheet has a field defined by a cured planar surface portion and at leastone noncured longitudinal edge area bordering the field and defined bythe extent of overlap of adjacent roofing membranes when installed on aroof deck.

[0008] The selectively cured sheets of EPDM membrane may be joined byproviding at least two sheets formed of ethylene-propylene dienetermonomer, the sheets having a field defined by a cured planar surfaceportion and at least one noncured longitudinal edge area bordering thefield defined by the extent of overlap of adjacent roofing membraneswhen installed on a roof deck. The noncured edge areas of two EPDMroofing membranes are then overlapped and pressed together and then theedge areas are vulcanized to splice the edge areas together.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Further features and other objects and advantages of thisinvention will become clear from the following detailed description madewith reference to the drawings in which:

[0010]FIG. 1 is a perspective view of the apparatus for selectivelycuring a sheet of EPDM;

[0011]FIG. 2 is an end view of the apparatus of FIG. 1; and

[0012]FIG. 3 is a partial end view of the apparatus of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Referring to the figures, wherein like reference charactersrepresent like elements there is shown an apparatus for selectivelycuring a sheet of EPDM to form a roofing membrane for installation on aroof deck. The sheet includes a field and longitudinal edges borderingthe field. The term “field” refers to the planar surface center area ofthe sheet of EPDM that is adjacent the longitudinal edge area of themembrane that forms the splice. It will be appreciated that thelongitudinal edge area that forms the splice may extend 2-3 inches fromthe edge of the sheet of EPDM. The term “EPDM” is intended to mean aterpolymer of ethylene-propylene and diene monomer. Illustrative methodsfor preparing such terpolymers are found in U.S. Pat. No. 3,280,082, thedisclosure of which is incorporated herein by reference. The preferredpolymers have from about 60 to about 95 weight percent ethylene and fromabout 0 to about 12 weight percent, preferably about 4 to about 6 weightpercent of the diene with the balance of the polymer being propylene orsome other similar olefin type polymer.

[0014] The diene monomer utilized in forming the EPDM terpolymer ispreferably a non-conjugated diene. Illustrative examples ofnon-conjugated dienes which may be employed are dicyclopentadiene,alkyldicyclopentadiene, 1,4-pentadiene, 1,4-hemadiene, 1,5hexadiene,1,4-heptadiene, 2-methyl-1,5-hexadiene, cyclooctadione, 1,4-octadiene,1,7-octadiene, 5-ethylidene-2-nor-bornene, 5-n-propylidene-2-norbornene,5-(2-methyl-2-butenyl)-2-norbornene and the like. A typical EPDM isVistalon® MD-744 (Exxon Chemical Co.) a terpolymer having a MooneyViscosity (ML/4 at 125 C.) of about 52; an ethylene/propylene (E/P)ratio of 61/39 weight percent and about 2.7 weight percent ofunsaturation.

[0015] Particularly useful and preferred in preparing a sulfur curableEPDM composition is Royalene® 3180 (Uniroyal Chemical Co.) which has aMooney Viscosity (ML/4 at 120° C.) of about 54; an ethylene/propyleneratio of about 67/33 weight percent; about 2.2 weight percent ofunsaturation (5-ethylidene-2-norbornene); about 2.7 percent by weight ofcrystallinity and a weight average molecular weight of approximately313,000 to 355,000. Also useful are thermoplastic heat seamable sheetingmaterials, i.e., EPDM's having a high degree of crystallinity as opposedto amorphous (non-crystalline) EPDM's. Examples thereof includeRoyalene® 375 (Uniroyal Chemical Co.); and EPsyn® 5508.

[0016] The composition employed to form the sheeting material comprises100 parts by weight of EPDM or other similar olefinic type polymers,including mixtures of two or more types, to which are added fillers andprocessing materials as well as curatives as well known in the art. Thecuratives include, for example, organic polyamines, organic polyacids,organic polyesters, organic polyanhydrides, organic polysulfides andprecursors thereof.

[0017] With respect to the fillers, suitable fillers are selected fromthe group consisting of reinforcing and non-reinforcing materials, andmixtures thereof, as are customarily added to rubber. Examples includesuch materials as carbon black, ground coal, calcium carbonate, clay,silica, cryogenically ground rubber and the like. Preferred fillersinclude carbon black, ground coal and ground recycled rubber orcryogenically ground rubber. Carbon black is used in an amount of about20 parts to about 300 parts per 100 parts of polymer (phr), preferablyabout equal to the amount or carbon black normally used in preparingsulfur cured EPDM roof sheeting. The carbon black useful herein is anycarbon black. Preferred are furnace blacks such as GPF (general purposefurnace), FEF (fast extrusion furnace) and SRF (semi-reinforcingfurnace).

[0018] The ground coal employed as a filler in the compositions of theinvention is a dry, finely divided black powder derived from a lowvolatile bituminous coal. The ground coal has a particle size rangingfrom a minimum of 0.26 microns to a maximum of 2.55 microns with theaverage particle size of 0.69±0.46 as determined on 50 particles, usingTransmission Electron Microscopy. The ground coal produces an aqueousslurry having a pH of about 7.0 when tested in accordance with ASTM D-1512. A preferred ground coal of this type is designated Austin Blackwhich has a specific gravity of 1.22±0.03, an ash content of 4.58% and asulfur content of 0.65%. Austin Black is commercially available fromCoal Fillers, Inc., P.O. Box 1063, Bluefield, Va. Amounts range fromabout 5 to 65 p˜ with about 15 to 35 being preferred.

[0019] Finally, essentially any ground recycled rubber may be employedas a filler in the composition of the invention. The preferred groundrecycled rubbers are cryogenically ground EPDM, butyl, neoprene and thelike. A preferred cryogenically ground rubber is a cryogenically groundEPDM rubber. The preferred cryogenically ground EPDM rubber is a fineblack rubbery powder having a specific gravity of 1.129±0.015 and aparticle size ranging from about 30 to about 300 microns with an averageparticle size ranging from about 50 to about 80 microns. Amounts rangefrom about 5 to 40 phr with about 10 to 25 phr being preferred.

[0020] Mixtures of Austin black and cryogenically ground rubber usefulherein may be utilized as a partial replacement for carbon black. Wheremixtures of these two fillers are employed the relative amounts thereofcan be widely varied; the overall total not exceeding about 60 phr. Theratio of Austin black to cryogenically ground rubber may range from adesired ratio of 2:1 to perhaps even a ratio of 3:1. Again, as notedhereinabove, other filler materials can be employed. Amounts of thesefiller materials fall within the range of amounts normally employed inpreparing sulfur cured conventional roof sheeting.

[0021] With respect to the processing material, it is included toimprove the processing behavior of the composition (i.e. reduce mixingtime and increase rate of sheet forming and includes processing oils,waxes and the like). The processing oil is included in an amount rangingfrom about 20 parts to about 150 parts process oil per 100 parts EPDMingredient phr, preferably in an amount ranging from about 60 to about100 phr. A preferred processing oil is a paraffinic oil, e.g. Sunpar2280 which is available from the Sun Oil Company. Other petroleumderived oils including naphtheuic oils may be used.

[0022] Optional ingredients include, for example, other elastomers(e.g., butyl elastomer, neutralized sulfonated EPDM, neutralizedsulfonated butyl) in place of minor amounts of the EPDM, secondaryinorganic fillers (e.g., talc, mica, clay, silicates, whiting) withtotal secondary filler content usually ranging from about 10 to about150, about 0.3 to 2 phr. It is a feature of the present invention thatthe roof sheeting compound is selectively cured prior to application.

[0023] The compounding ingredients can be admixed, utilizing an internalmixer (such as a Banbury mixer), an extruder, and/or a two-roll mill, orother mixers suitable for forming a viscous relatively uniformadmixture. When utilizing a type B Banbury internal mixer, in apreferred mode, the dry or powdery materials such as carbon black areadded first followed by the liquid process oil and finally the polymer(this type of mixing can be referred to as an upside-down mixingtechnique).

[0024] The resulting admixture is continuously sheeted to a thicknessranging from 5 to 200 mils, preferably from 35 to 60 mils, byconventional sheeting methods, for example, milling, calendering orextrusion. Preferably, the admixture is sheeted to at least 40 gauge(0.040 inches) which is the minimum thickness specified in standards setby the Roofing Council of the Rubber Manufacturers Association fornon-reinforced black EPDM rubber sheets for use in roofing applications.In many cases, the admixture is sheeted to 40-45 gauge thickness sincethis is the thickness for a large percentage of “single-ply” roofingmembranes used commercially.

[0025] Referring to FIGS. 1-3, the apparatus 10 includes a curing oven12 having a radiation source 14 and at least one screen 16. It will beappreciated that most any suitable curing oven design may be used toselectively cure at least the field of a sheet 18 of EPDM. The curingoven 12 may be formed of most any suitable material to withstand thehigh temperatures experienced in the curing oven. In a preferredembodiment, the curing oven 12 includes a means to continuously conveythe sheet 18 of EPDM through the oven, a radiation source 14 and ascreen 16 to shield at least a portion of the radiation from the sheet18 of EPDM.

[0026] The apparatus 10 includes a curing oven 12 having a roof 20 and afloor 22 interconnected by sidewalls 24, a front end 26 and a back end28. The front end 26 of the curing oven 12 includes an entrance 30 andthe back end 28 of the curing oven includes an exit 32. Positionedbetween the front end 26 and the back end 28 of the curing oven 12 is anendless conveyor 34 of a type well known in the art for continuouslyconveying the sheet 18 of EPDM through the curing oven. Operativelyprojecting from each sidewall 24 of the curing oven 12 is at least onescreen 16. The screen 16 may extend the longitudinal length of thecuring oven 12 or a plurality of screens may project from each sidewallto form a continuous shield as further described herein. The screen 16is a flat, rectangular shape radiation reflective material of a typewell known in the art to cover the edge area 36 of the sheet 18 of EPDMforming the splice. The screen 16 acts to shield the edge area 36 of thesheet 18 of EPDM as the sheet passes through the curing oven 12 underthe radiation source 14. In a preferred embodiment, the curing oven 12includes an actuating member 38 to operatively position the screen 16between an extended position over the edge area 36 of the sheet 18 ofEPDM as shown in FIG. 1 to a retracted position as shown in FIG. 3. Theactuating member 38 includes a piston member and an arm attached to thescreen. However, it will be appreciated that the actuating member 38 maybe most any suitable mechanical linkage of a type well known in the artto move the screen 16 from an extended position to a retracted positionand back.

[0027] Located above the conveyor 34 within the curing oven 12 is aradiation source 14. The radiation source 14 provides a desired dose ofhigh-energy radiation to cure at least the exposed field 40 of the sheet18 of EPDM. Typically, useful high-energy sources of radiation includeinfrared radiation, gamma rays, x-rays, beta rays and the like. In apreferred embodiment, the radiation source 14 includes an array ofinfrared heat lamps of a type well known in the art located above theconveyor 34 within the curing oven 12. The intensity of the high energyradiation must be sufficient to crosslink the polymers within the sheet18. Preferably, the intensity of the high energy radiation must be suchthat that the surface temperature of the sheet 18 is at least about 204°C.

[0028] In operation, the sheet 18 of EPDM is conveyed from a roller headdie extruder 42 or similar device to manufacture the sheet, to thecuring oven 12. The sheet 18 of EPDM then enters the entrance 30 of thefront end 26 of the curing oven 12 and is conveyed through the curingoven beneath the radiation source 14. At least one, and preferably two,of the screens 16 are positioned above the edge areas 36 of the sheet ofEPDM to shield the area. The radiation source 14 continuously cures atleast the field 40 of the sheet 18 of EPDM as the sheet is conveyedthrough the curing oven 12. The selectively cured sheet 18 of EPDM exitsthe back end 28 of the curing oven 12 to a take-up roll as well known inthe art.

[0029] The selectively cured sheet 18 of EPDM forming a roofing membranemay be spliced together by overlapping and pressing the noncured edgeareas 36 of two EPDM roofing membranes together and then vulcanizing theedge areas to splice the edge areas together. It will be appreciatedthat by selectively curing at least the field 40 of the sheet 18 ofEPDM, the EPDM roofing membranes may be spliced together without usingan adhesive.

[0030] The patents and documents described herein are herebyincorporated by reference.

[0031] Having described presently preferred embodiments of theinvention, the invention may be otherwise embodied within the scope ofthe appended claims.

What is claimed is:
 1. A method for selectively curing a sheet ofethylene-propylene diene termonomer (EPDM) material to form a roofingmembrane for installation on a roof deck comprising the steps of:providing a sheet formed of ethylene-propylene diene ternonomer, thesheet having a field and two longitudinal edge areas bordering thefield; and simultaneously shielding at least one edge area of the EPDMsheet and exposing at least the field to a source of radiation to cureat least the field of the EPDM sheet and provide a selectively curedEPDM roofing membrane.
 2. The method of claim 1 wherein the sheet isprovided by milling, calendering or extrusion.
 3. The method of claim 1wherein the sheet is from 5 to 200 mils thick.
 4. The method of claim 1wherein two longitudinal edge areas of the EPDM sheet are shielded. 5.The method of claim 1 wherein the at least one longitudinal edge area ofthe EPDM sheet is shielded by operatively projecting at least one screenover the at least one longitudinal edge area of the sheet and shield theedge area of the sheet of EPDM.
 6. The method of claim 1 wherein twolongitudinal edge areas of the EPDM sheet are shielded by operativelyprojecting a screen over each longitudinal edge area of the sheetthereby shielding the edge area of the sheet of EPDM.
 7. The method ofclaim 1 wherein the source of radiation is infrared radiation.
 8. Anapparatus for selectively curing a sheet of ethylene-propylene dienetermonomer (EPDM) material, the sheet having a field and longitudinaledge areas bordering the field, the apparatus comprising: a curing ovenhaving a roof and a floor interconnected by sidewalls, a front end and aback end, the front end including an entrance and the back end includingan exit, a conveyor positioned between the front end and the back end ofthe curing oven for continuously conveying the sheet of EPDM through thecuring oven; a radiation source located above the conveyor within thecuring oven; and at least one screen operatively projecting from eachsidewall of the curing oven and extending the longitudinal length of thecuring oven to cover at least one edge area of the sheet and shield theedge area of the sheet of EPDM as the sheet passes through the curingoven under the radiation source.
 9. The apparatus of claim 8 wherein thescreen is a flat, rectangular shape radiation reflective material. 10.The apparatus of claim 8 wherein the curing oven includes an actuatingmember to operatively position the screen between an extended positionover the edge area of the sheet of EPDM to a retracted position.
 11. Theapparatus of claim 10 wherein the actuating member includes a pistonmember and an arm attached to the screen.
 12. The apparatus of claim 8wherein the radiation source provides a desired dose of high-energyradiation to cure at least the exposed field of the sheet of EPDM. 13.The apparatus of claim 12 wherein the radiation source is selected frominfrared radiation, gamma rays, x-rays, or beta rays.
 14. The apparatusof claim 12 wherein the radiation source includes an array of infraredheat lamps positioned above the conveyor within the curing oven.
 15. Amethod of joining selectively cured sheets of EPDM membrane comprisingthe steps of: providing at least two sheets formed of ethylene-propylenediene termonomer, the sheets having a field defined by a cured planarsurface portion and a noncured longitudinal edge area bordering thefield defined by the extent of overlap of adjacent roofing membraneswhen installed on a roof deck; and then overlapping and pressing thenoncured edge areas of two EPDM roofing membranes together and thenvulcanizing the edge areas to splice the edge areas together.
 16. Aroofing membrane comprising: a sheet formed of ethylene-propylene dienetermonomer (EPDM) material, the sheet having a field defined by a curedplanar surface portion and a noncured longitudinal edge area borderingthe field and defined by the extent of overlap of adjacent roofingmembranes when installed on a roof deck.